1. Field of the Invention
The present invention relates to a tunable anti-Stokes Raman laser (ASRL) and, more particularly, to a tunable anti-Stokes Raman laser capable of generating ultraviolet (UV) ASRL emission in a medium of inverted neutral indium atoms.
2. Description of the Prior Art
An anti-Stokes Raman laser may be defined as stimulated anti-Stokes Raman emission induced by a pump laser between two levels of the same parity in which a population inversion exists between the upper and lower Raman states. Such laser devices are particularly attractive since they are tunable by tuning the pump laser. Additionally, since the upper Raman state is often a metastable level, large inversion densities and high anti-Stokes output energies are possible. Early work in this area is reported in an article entitled "Observation of Stimulated Anti-Stokes Raman Scattering in Inverted Atomic Iodine", by R. L. Carman et al appearing in Physical Review Letters, Vol. 33, No. 4, July 22, 1974, at pp. 190-193. As described therein, measurable gain in inverted I atoms may be obtained, where the I*(5p.sup.5 2P.degree..sub.1/2) state is populated by flash photolysis of trifluoromethliodide (CF.sub.3 I). The anti-Stokes Raman signal may be observed by pumping this inversion with the fundamental of a Nd:YAG (yttrium aluminum garnet) laser at 1.06 .mu.m and probing with a broadband dye laser. The article goes on to state, however, that superfluorescent emission at the nonresonant anti-Stokes wavelength was not observed during these experiments.
Previously, anti-Stokes Raman lasers have been constructed by the present inventor based upon metastable population inversion in three atomic species, namely thallium, iodine, and bromine, where such work is disclosed in U.S. Pat. Nos. 4,486,884, 4,504,949, and Ser. No. 474,566, previously issued to the present inventor and assigned to the present assignee. Various articles have also been published which relate to this previous work, where two of these references are article entitled "Anti-Stokes Raman Laser", by J. C. White et al appearing in Physical Review A, Vol. 25, at pp. 1226-1229 and "Tunable, 178 nm Iodine Anti-Stokes Raman Laser", by J. C. White et al appearing in Optical Letters, Vol. 7, May 1982, at pp. 204-206. Optical Letters, Vol. 7, May 1982, at pp. 204-206. These above-cited articles describe experiments which have demonstrated several of the attractive features of the anti-Stokes Raman laser concept, including large density metastable storage, long population storage times, tunability of the upconverted anti-Stokes laser, and high conversion efficiency.
U.S. Pat. No. 3,991,387 issued to R. W. Waynant on Nov. 9, 1976, discloses a method of synchronous generation and amplification of tunable VUV laser radiation. The Waynant system uses a flat plate electrical transmission discharge system as a combination radiation generating pump laser (N.sub.2 laser) and a short wavelength amplifier. One channel generates the N.sub.2 pump laser which excites a pair of dye cells generating two tunable dye laser frequencies in the near UV. The two frequencies are made co-linear and passed into a gas or vapor cell to additively produce a resultant vacuum ultraviolet signal. The vacuum ultraviolet signal is transmitted to a second channel where it is injected into the second channel simultaneous with gain in the flat plate electrical system. The signal is amplified sufficiently that additional mixing can take place. A necessary feature of this arrangement, however, is the utilization of two frequencies in the near UV to generate the VUV radiation. An alternative arrangement for generating VUV radiation is disclosed in U.S. Pat. No. 4,218,628 issued to S. E. Harris on Aug. 19, 1980. In the Harris arrangement, spontaneous anti-Stokes scattering from an atomic populations stored in a metastable level is utilized to generate the VUV radiation.
All of the above-described research has dealt with the creation of an anti-Stokes Raman laser from an ionic species, where an initial step is needed in the process to create an ionic population from the ground state neutral atoms.